Heat pipe having improved dielectric strength

ABSTRACT

The disclosed heat pipe includes a hermetically sealed housing having two portions electrically insulated from one another and maintained at differing electrical potentials. Contained within the housing is a volatile working fluid, a capillary wick and an inert gas having relatively high dielectric strength. Sufficient inert gas is contained within the housing to maintain a predetermined breakdown voltage at the lowest temperature of operation of the heat pipe.

United States Patent [72] Inventor Algerd Basiul'm Redondo Beach, Calif.[21] Appl. No. 759,854 [22] Filed Sept. 16, 1968 [45] Patented Feb. 16,1971 [73] Assignee Hughes Aircraft Company Culver City, Calif. acorporation of Delaware [54] HEAT PIPE HAVING IMPROVED DIELECTRICSTRENGTH 8 Claims, 10 Drawing Figs. [52] 1.1.8. (I 165/105, 165/32;174/15; 313/12, 313/44; 317/234 [51] Int. Cl 28d 15/00, H01 j 7/24 [50]Field ofSeareh 165/105; 317/234; 174/15; 313/12, 44; 62/514 [56]References Cited UNITED STATES PATENTS 3,229,759 l/1966 Grover 165/1053,382,313 5/1968 Angello 174/15 Primary Examiner-Robert A. OLearyAssistant Examiner-Albert W. Davis, Jr. Attorneys-James K. Haskell andPaul M. Coble ABSTRACT: The disclosed heat pipe includes a hermeticallysealed housing having two'portions electrically insulated from oneanother and maintained at differing electrical potentials. Containedwithin the housing is a volatile working fluid, a capillary wick and aninert gas having relatively high dielectric strength. Sufficient inertgas is contained within the housing to maintain a predeterminedbreakdown voltage at the lowest temperature of operation of the heatpipe.

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PATENTED FEB 1 6 I971 SHEET 8 OF 6 Fig. 7.

HEAT PIPE HAVING IMPROVED DIELECTRIC STRENGTH This invention relates toheat pipes, and more particularly relates to a heat pipe having a highdielectric strength so as to maintain a predetermined breakdown voltageat low temperature operating ranges.

Heat pipes are often used to transfer thermal energy from a first regionto a second region by means of heat exchange so as to cool the firstregion, for example. This energy exchange may be made through any mediumthat conducts heat. One effective way to achieve this energy exchange isto employ a suitable fluid that assimilates energy at the first regionwhen the fluid vaporizes; then, after traveling in vapor form to thesecond region, releases the energy there by condensation. Return of thefluid in its liquid form to the first region may be accomplished bymeans of gray or capillary action, for example.

It is often desirable to transfer energy by heat exchange from a surfacemaintained at one electrical potential to a surface at a substantiallydifferent electrical potential. Since heat pipe fluid is normallycontained within a hermetically sealed chamber, when the temperatureinside of the chamber is reduced, the pressure of the fluid vapor insideof the chamber is also reduced; thus the dielectric strength (themaximum potential gradient a material can withstand without rupture) ofthe fluid vapor is decreased. Prior art heat pipe cooling systems haveemployed bellow or similar devices to maintain the fluid vapor at aconstant pressure in order to maintain the desired dielectric strengthof the fluid vapor at low temperatures. Alternatively, heaters have beenused to heat the fluid vapor so as to increase its pressure prior to theoperation of the heat pipe. For applications where available space isminimal and where reliability of operation must be extremely high (suchas the cooling of electronic equipment contained within a spacesatellite), such heat pipe arrangements not practical.

Accordingly it is an object of the present invention to provide a heatpipe having improved dielectric strength so as to maintain apredetermined high breakdown voltage at low temperatures.

It is a still further object f the present invention to provide a highdielectric strength heat pipe that is simple and economical tomanufacture.

It is yet another object of the present invention to provide a highdielectric strength heat pipe that occupies minimal space, that is lightin weight, and is reliable in operation.

In accordance with the foregoing objects, a heat pipe according to theinvention includes a hermetically sealed housing having two portionsthat are electrically insulated from each other. A capillary wick isdisposed along the inner surface of the sealed housing. Contained withinthe housing and within at least a portion of the wick is a volatileworking fluid. Also contained within the housing is preselected quantityof a substantially chemically inert gas having a dielectric strengthgreater than that of the working fluid when in the vapor state at apredetermined operating temperature.

Additional objects, advantages and characteristic features of thepresent invention will become more readily apparent from the followingdetailed description of preferred embodiments of the invention whenconsidered in conjunction with the accompanying drawings in which:

FIGS. la, lb, and 1c are longitudinal sectional views illus-.

trating the construction and operation of a heat pipe according to anembodiment of the invention;

FIG. 2 is a graph showing the breakdown voltage as a function oftemperature for two exemplary operative fluids for a heat pipe accordingto the invention;

FIGS. 3 and 4 are longitudinal sectional views illustrating heat pipesaccording to further embodiments of the invention;

FIG. 5 is a longitudinal sectional view illustrating a heat pipeaccording to still further embodiment of the invention;

FIG. 5a is a cross-sectional view taken along line 5a-5a of FIG. 5;

FIG. 6 is a longitudinal sectional view illustrating a heat pipeaccording to a still further embodiment of the invention; and

FIG. 7 is a schematic diagram illustrating a method of manufacturing aheat pipe according to the invention.

5 Referring to FIG. la with greater particularity, a heat pipe accordingto the invention, designated generally by the numeral 11, includes ahousing 10. Housing 10 may be essentially cylindrical in shape, forexample, and may have first and second elongated electrically conductiveportions and 16 separated by a ring 18 of electrically insulativematerial so that portions 15 and 16 may be maintained at substantiallydifferent electrical potentials. One end of housing 10 is provided witha vacuum stem 12, which when sealed off allows heat pipe 11 to becomehermetically sealed. A capillary wick 20, which may be the form ofseveral strips or a solid sheet, for example, is disposed along theinner surface of housing 10. The wick 20 may be of a material (such asnylon, paper, glass fiber, silicon dioxide, porous ceramics,ceramic-metal fiber components, or combinations of the foregoing, forexample) having sufficient electrically insulating properties towithstand any practical potential difference between housing portions 15and 16. Wick 20 may be force fit into housing 10, or riveted, sinteredor soldered thereto, for example Wick 20 is saturated with anappropriate working fluid that vaporizes in vapor space 22 enclosed byhousing 10. Contained within vapor space 22 is not only the workingfluidvapor (represented in FIG. 1 by circles 24) but also apredetermined quantity of inert gas (represented in FIG. 1 by xs 26).This inert gas is essential in maintaining a predetermined breakdownvoltage between housing portions 15 and 16 at the lower operatingtemperatures of the heat pipe.

Therefore, the inert gas 26 has dielectric strength and a boiling pointhigher than those of the working fluid vapor at the aforementioned loweroperating temperatures. The amount of working fluid in the heat pipe 11should be, as nearly as possible, equal to, if not in excess of, thevoid wick volume (i.e., the amount of fluid which the wick will holdwhen saturated) of wick 20 since too little fluid will prohibitefficient energy exchange by heat transfer.

One of several factors to consider in selecting an appropriate workingfluid is the dielectric strength of the fluid when in either vapor orliquid states anjd the desired temperature range of operation of theheat pipe'f'Other factors desirable in a working fluid are a high latentheat of vaporization for maximum energy transfer ability, low viscosityfor reduced internal fluid friction, and high surface tension and goodwetting ability of the wick material for a high capillary force. Anonexclusive list of possible working fluids with their appropriatetemperature ranges is given below:

Approximate dielectric strength Approximate at atmospheric pressure androom useful tem- Working fluid temperature (Approx. 25 C.) perature mpg?Dowtherm A CP-63 500 volts/mil Not available Freon 12 .do

cylindrical shell closed at one end and attached to the adjacent innersurfaces of housing alternatively, wick 20 may consist of a plurality ofwick strips extending longitudinally along the inner surfaces of housing10 from portion to portion 16. Channels, screens, cloths or sinteredstructures made of the aforementioned wick materials or combinationsthereof, for example, may be use for the wick configuration.

Wick thickness is also an important design consideration. An excessivelythick wick will impede the flow of heat transversely through the wick;on the other hand if the wick is too thin, the capillary flow of thecondensed working fluid will be impeded. Furthermore, the length 'ofwick should be minimized in order to reduce pressure drop in thecondensed working fluid. The desired length of the wick is a function ofthe wick pore size and the type of working fluid used. For example, fora wick made of silicondioxide and with Dowtherm A being used as theworking fluid, when the working fluid is flowing in the wick against theforce of gravity (i.e., the heat pipe is being operated in a verticalattitude) the wick length may be approximately 6 inches and the wickthickness approximately one-eight of an inch.

The breakdown voltage between housing portions 15 and 16 (i.e., thevoltage at which portions 15 and 16 are no longer electrically insulatedfrom one another) is dependent on the dielectric strength of the fluidin vapor space 22, the distance between the surfaces over whichbreakdown may occur, and the shape of the surfaces over which breakdownoccurs (assuming wick 20 has a higher dielectric strength than the fluidin space 22). Disregarding the shape of portions 15 and 16, byincreasing the width of insulating ring 18 and thereby the distancebetween portions 15 and 16, the breakdown voltage for a given pressureis increased. Therefore, it is advantageous to make ring 18 as wide asis possible.

The gas 26 used in a heat pipe according to the -invention should besufficiently chemically inert so that it will not interfere with theoperation of the heat pipe. The more chemically inert the gas, thelonger the operational life of the heat pipe. Another criteria inselecting an appropriate inert gas is its dielectric strength at thelowest temperature range of operation of the heat pipe. The dielectricstrength of the inert gas over this temperature range should be greaterthan the dielectric strength of the working fluid vapor over the sametemperature range. It is also necessary that the inert gas have aboiling point lower than that of the working fluid so as to minimizeinterference with the heat transfer by the working fluid. In addition,the inert gas should be substantially insoluable in the working fluid.Typical examples of appropriate inert gases to be used in conjunctionwith the aforementioned exemplary working fluids N SF C F C F C P and CF The exact amount of inert gas to be used in heat pipe 11 depends onthe particular gas and working fluid used as well as on the breakdownvoltage at a desired temperature. For example, assume that SF gas isused as the inert gas, Dowtherm A is used as the working fluid, and thata breakdown voltage of not less than 15k volts is desired for a 0.200inch spacing between portions 15 and 16 at their point of closestproximity over an operating temperature from room temperature C.approximately) to about 250C. The breakdown voltage of Dowtherm A vaporat room temperature and at pressures near atmospheric pressure issubstantially below the aforementioned breakdown voltage of 15k volts.However, the breakdown voltage of a mixture of Dowtherm A and SP gas atthe same temperature and at a pressure of 300 mm. Hg. is approximatelyISK volts. In order to maintain the breakdown voltage of the heat pipeabove 15K volts at all temperatures of operation, sufficient SF gas mustbe introduced into the heat pipe housing 10 so that the total internalvapor pressure at the lowest operating temperature of the heat pipe is300 mm. Hg.

Typical heat pipe vapor cavity breakdown voltage vs. temperaturecharacteristics are illustrated in FIG. 2. Curve 32 shows thecharacteristic for a heat pipe employing a mixture of Dowtherm A and SF.gas (at 300 mm. Hg. pressure at room temperature); curve 34 shows thecharacteristic for Dowtherm A alone.

The operation of a heat pipe according to the invention will now beexplained with reference to FIGS. 10, lb and Ir. FIG. 1a represents theheat pipe at ambient temperature with an amount of inert gas 26, asdiscussed above, intermixed with vaporized working fluid 24. As heat isapplied to portion 15 (FIG. 11:), working fluid in adjacent regions ofthe wick 20 is evaporated. Working fluid vapor 24 then travels towardportion 16, since portion 16 is at a lower temperature than portion 15.As the working fluid vapor travels from higher temperature portion 15toward the lower temperature portion 16, the kinetic energy of theworking fluid vapor "pushes" the inert gas toward portion 16. At or inthe vicinity of portion 16, the working fluid vapor condenses, therebytransferring heat through wick 20 and housing 10. The condensed workingfluid is then, by capillary force, drawn back through wick 20 towardportion 15 where it is once again evaporated. When the heat pipe isoperating at maximum heat transferring capacity (FIG. 1c), the kineticenergy of the working fluid vapor "pushes" the inert gas to the end ofthe heat pipe adjacent vacuum stem 12. The amount of space occupied bythe inert gas is proportional to the kinetic energy of the working fluidvapor. Minimal interference with the movement of the hat transferringworking fluid vapor by the inert gas is thereby achieved. Only a smallportion of the effective length of the heat pipe is thus sacrificed forheat transfer purposes, while orders of magnitude increases in thedielectric strength of the heat pipe can be achieved at low operatingtemperatures.

The exact structure of a heat pipe according to the invention may bemodified so as to be especially suitable for a particular heat transferoperation.

FIG. 3 illustrates a cross section of a heat pipe according to theinvention which may be used to remove heat from a substantiallycylindrical member 36, which may be the collector of a traveling-wavetube, for example, and which is maintained at a desired electricalpotential. Electrically insulating ring 38 insulates heat input portion44 of a heat pipe housing 42 from a heat output portion 40 of housing42. Heat input portion 44 is in contact with the member 36 to be cooled,and thus resides at the same electrical potential as the member 36,while the heat output portion 40 resides at a substantially differentelectrical potential, for example ground. Heat pipe housing 42 enclosesa hermetically sealed vapor cavity 41. A fluid evaporating wick 46 isdisposed substantially along the surface of housing portion 44 facinginto vapor cavity 41, while a fluid condensing wick 48 is disposedsubstantially along the surface of housing portion 40 facing into vaporcavity 41. Alternatively, housing portion 44 may be partiallyeliminated, and wick 46 disposed in contact with the outer surface ofmember 36. A plurality of electrically insulating spoke wicks 50 connectwicks 46-and 48 to facilitate the return of working fluid evaporatedfrom wick 46 and condensed in wick 48 to wick 46 by means of capillaryaction. Wicks 50 may be spokes, wedges or annular members, for example,the particular shape of the wicks 50 not being critical.

The heat pipe of FIG. 3 functions in a manner similar to that of FIGS.la, lb and 1c. The kinetic energy of working fluid vapor moleculestraveling from the vicinity of member 36 toward housing portion 40 isgenerally sufficient to maintain the inert gas away from the major heattransfer region during operation of the heat pipe if the workingfluid-inert gas interface area is relatively small. For larger interfaceareas, however, an interface shield 52 may be inserted into the heatpipe vapor cavity 41 to enhance the separation between the two fluids.Shield 52 minimizes the interface area by allowing inert gas-workingfluid contactonly along gas passageways 53.

It is often desirable to operate a heat pipe at various attitudes inrelation to the direction of a force field, such as gravity, forexample. Since the heat pipe Since the heat pipe operates by capillaryforce, the effect of gravity may impede the capillary action within thecondensing portion of the wick. For the heat pipe of FIG. 3, if anelectrically insulative siphon wick 58 is employed as shown, the heatpipe may be operated substantially independently of a force field suchas gravity. assuming the force field exists in a direction illustratedby arrow 55.

For steady state heat pipe operation, the following equationapproximates the factors which affect the flow of working fluid withinthe wicks: AP AP AP, AP, (1) where AP is the capillary driving pressure,AP, is the pressure drop along wick 48 caused by the vapor flow, AP isthe pressure drop due to the working fluid liquid flow, and AP, is thepressure drop along wick 48 due to gravity. The capillary drivingpressure within wick 48 must be sufficient to support the column offluid within it, otherwise the fluid will flow out of wick 48 into vaporspace 41. Wicks 46 and 50 and the portion of wick 48 within region A actas a U-tube, and consequently a siphon effect overcomes the pressuredrop due to gravity. If a quantum of fluid condenses in wick 48 inregion B, a siphon U- tube effect will be created by means of wick 48and siphon wick 58. Therefore, the heat pipe'may be operatedsubstantially free from the effect of gravity.

Since vapor space 41 contains a dielectric material (the working fluidand the inert gas), when a potential difference exists between housingportions 40 and 44, a capacitance effect results. The amount ofcapacitance depends largely on the distance between portions 44 and 40,the greater the distance, the less the capacitance. If a limited amountof power is available to charge the resultant capacitor, 'as may be thecase in a space satellite, the distance between portions 40 and 44should be maximized. 7

FIG. 4 illustrates a modification of the heat pipe shown in FIG. 3; thereference numerals; designating corresponding parts in these twoembodiments are the same, except that for FIG. 4 the prefix numeral 1 isemployed. In the heat pipe illustrated in FIG. 4, shield 52 iseliminated and as a functional substitute therefor an inert gas holdingsection, or chamber, 154 is connected to vapor cavity 141 by means of athroat section 156 and a siphon wick 158. The inner surfaces of holdingsection 154 and of throat section 156 may be lined with extensions 148'and 148" respectively of wick 148. Holding section 154 is used tosubstantially remove the inert gas from the heat transfer areas whilethe heat pipe is operating; hence the inert gas temperature more closelyapproximates the ambient temperature.

The operation of the heat pipe illustrated in FIG. 4 is substantiallythe same as that of the heat pipe illustrated in FIG. 1. In steady stateoperation of the heat pipe, the working fluid vapor pushes" the inertgas into section 154 through throat 156 where it may be more easily heldat a temperature lower than the temperature in cavity 141. Lining theinner surfaces of section 154 and throat 156 with extensions 148' and148" of wick 148 facilitates the return of condensed working fluid towick 146. Wick 158, evaporating wick 146, condensing wick 148 and spokewicks 150 function to provide a siphonlike capillary path tosubstantially eliminate the effect of gravity on the operation of theheat pipe as discussed above.

FIGS. 5 and 5a illustrate a modification of the heat pipe shown in FIG.4. The last two reference numeral digits designating corresponding partsin these two embodiments are the same; however, for the FIG. 5-511embodiment the numeral 2 rather than 1 is used as the first referencenumeral digit. The heat pipe illustrated in FIGS. 5 and 5a operates inessentially the same manner as that of FIG. 4 but differs fromtheembodiment of FIG. 4 in that member 236 to be cooled has a substantiallydome-shaped end and that inert gas section, or chamber, 254 is annularlydisposed around the longitudinal axis of the heat pipe and extends bothradially outwardly of and longitudinally beyond housing 242. Housingportion 261 extends longitudinally from the outer wall of holdingsection 254 toward member 236 and is spaced from and annularly disposedabout housing 242 so as to form a cooling channel 260 for allowing asuitable coolant such as air, for example, to absorb heat from the outersurfaces of housing 242. A plurality of housing throat sections 257extending into channel 260 connect holding section 254 with vapor cavity241.

In order to allow working fluid that condenses in section 254 to returnto wick 246, either a siphon wick 258 may be used to connect wick 248with wick 246, or the inner surfaces of throat sections 257 may be linedwith extension 241" of wick 248. When a greater working fluid capillaryflow capacity is desired both arrangements may be employedsimultaneously. Since member 236 may extend a substantial distance intovapor cavity 241 the length of cavity 241 may be extended to accommodatethe additional length, and additional spoke wicks 250 may be employed toensure uniform distribution of working fluid over evaporating wick 246.

FIG. 6 illustrates a modification of the heat pipe of FIG. 5. The lasttwo referencenumeral digits designating corresponding parts in these twoembodiments are the same, however, for the FIG. 6 embodiment the numeral3 rather than 2, is used as the first reference numeral digit. Theembodiment illustrated in FIG. 6 differs from that illustrated in FIG. 5principally in that member 336 is an elongated shaft or tube whosesurface requires heat removal and that inert gas holding section, orchamber, 354 is substantially longitudinally coextensive with heat pipehousing 342. As with the embodiment of FIG. 5, holding section 354 isannularly disposed around heat pipe housing 342 and spaced therefrom soas to form a cooling channel 360 between the inner surface of section354 and the outer surfaces of housing 342. A plurality of radiallydisposed throats 357 extend into channel 360 and connect vapor cavity341 and gas holding section 354.

Heat pipes according to the invention may be used to remove heat from avariety of electronic devices. For example, the embodiments of theinvention illustrated in FIGS. 3, 4 and 5-50 could be used to cool thecollector or the electron gun portions of a traveling-wave tube. Theembodiment illustrated in FIG. 6 may be used to cool the wave-electronbeam interaction section of a traveling-wave tube, for example.

Referring to FIG. 7, in order to manufacture a heat pipe according tothe present invention, a heat pipe assembly 62 (which for purpose ofexplanation is illustrated as the heat pipe 11 of FIG. 1) is attached bystem 17 to one end ofa pipe 64. The other end of pipe 64 communicateswith a vacuum pump 65 and via an auxiliary pipe 64a with an inert gascontainer 66. A first valve 68 is used to hermetically isolate the inertgas container 66 and pump 65 from the heat pipe assembly 62. A secondvalve 70 is employed to hermetically isolate the pump 65 fromcontainer.66 and heat pipe assembly 62. A third valve 72 hermeticallyisolates inert gas container 66 from pump 65 and assembly 62. A pressureguage 74 is connected to the interior of the pipe 64 between the valves68, 70 and 72.

In manufacturing a heat pipe according to the invention, the properamount of working fluid is first inserted into the heat pipe assembly62. Next, unwanted fluids are removed from the heat pipe. This removalmay be accomplished by vacuum pumping the vapor cavity 19 of assembly 62by means of pump 65. Escape of working fluid from assembly 62 duringvacuum pumping may be minimized by means of a heated venturi section 76of pipe 64. When venturi section 76 is heated to a higher temperaturethan assembly 62, escaping working fluid is returned to the assembly 62,During the vacuum pumping operation valves 68 and 70 are open whilevalve 72 is closed. v

The next step in manufacturing the heat pipe is to eliminate from pipe64 any substances that might later adversely affect the operation of theheat pipe. This may be accomplished by releasing inert gas into pipe 64(by opening valve 72), and then allowing pump 65 to clear thepipe 64 ofthe inert gas and any accompanying impurities (valve 70 open, valve 72closed). The impurity removal operation (during which time valve 68remains closed) may have to be repeated several times in order toeliminate substantially all impurities.

Finally, an amount of inert gas sufficient to maintain the heat pipe ata desired breakdown voltage is inserted into assembly 62. Assembly 62 iscooled to the heat pipe's minimum operating temperature, and inert gasis allowed to enter the heat pipe (valve 70 is closed while valves 68and 72 are opened) until the desired gas pressure (determined asdiscussed above) is attained. When the gas pressure within the heat pipereaches the desired value, as indicated on gauge 74,

valve 68 is closed, and assembly 62 is hermetically sealed at stem 17.

Although the present invention has been shown and described withreference to particular embodiments, nevertheless, various changes andmodifications obvious to a person skilled in the art to which theinvention pertains are deemed to lie within the spirit, scope andcontemplation of the invention.

Iclaim:

l. A heat pipe comprising:

a hermetically sealed housing having a heat input portion and a heatoutput portion and an electrically insulating portion disposed betweensaid input and said output portions;

first capillary wick means disposed within said housing substantiallyalong a surface of said heat input portion, second capillary wick meansdisposed within said housing substantially along a surface of said heatoutput portion, electrically insulating wick means connecting said firstand second wick means;

a volatile working fluid contained within said housing and within atleast portions of said wick means;

a substantially chemically inert gas contained with said housing andhaving a dielectric strength greater than the dielectric strength ofsaidfluid when in the vapor state at a predetermined operatingtemperature, said gas also having a boiling point below'that of saidfluid; and

means for enhancing separation of said fluid in the vapor state and saidgas when heat is being transferred from said heat input portion to saidheat output portion by means of said fluid.

2. A heat pipe according to claim 1 wherein said fluid is selected fromthe group consisting of Dowtherm A; FC43, Dowcorning 200, Freon 13, andFreon 12; and said inert gas is selected from the group consisting of NSP C F C 1 8, C,F,0 and C F 3. A heat pipe according to claim 1 whereinthe volatile working fluid contained within said housing is sufficientto substantially saturate each said wick means, and the quantity of saidinert gas disposed within said housing is sufficient to maintainelectrical insulation between said heat output portions at saidoperating temperature' 4. A heat pipe according to claim 1 wherein thelast named means is an interface shield disposed within said outputportion of said housing.

5. A heat pipe according to claim 1 wherein the last named meansincludes a chamber spaced from but operatively coupled to said heatoutput portion such that said gas may pass from said housing into saidchamber, whereby during the operation of said heat pipe said inert gassubstantially resides in said chamber and said working fluidsubstantially resides in said housing.

6. A heat pipe comprising:

a hermetically sealed housing of substantially tubular shape having aheat input portion and a heat output portion and an electricallyinsulating portion disposed between said input and said output portions;

first capillary wick means disposed within said housing substantiallyalong a surface of said heat input portion, second capillary wick meansdisposed within said housing substantially along a surface of said heatoutput portion, electrically insulating wick means connecting said firstand second wick means;

a volatile working fluid contained within said housing and within atleast portions of said wick means;

a substantially chemically inert gas contained with said housing andhaving a dielectric strength greater than the dielectric strength ofsaid fluid when in the vapor state at a predetermined operatingtemperature, said gas also having a boiling point below that of saidfluid;

a chamber annularly disposed around the longitudinal axis of saidhousing and extending both radially outwardly of and longitudinallybeyond said housing;

wall means spaced from the outer surface of said housing for forming inconjunction therewith a cooling channel for allowing the removal of heatfrom said housing; and

throat means extending into said channel for providing a passageway forthe flow of inert gas and working fluid between said housing and saidchamber.

7. A heat pipe comprising:

a hermetically sealed housing of a substantially tubular shape having aheat input portion and a heat output portion and an electricallyinsulating portion disposed between said input and said output portions;

first capillary wick means disposed within said housing substantiallyalong a surface of said heat input portion, second capillary wick meansdisposed within said housing substantially along a surface of said heatoutput portion, first electrically insulating wick means connecting saidfirst and second wick means;

a volatile working fluid contained within said housing and within atleast portions of said wick means;

a substantially chemically inert gas contained with said housing andhaving a dielectric strength greater than the dielectric strength ofsaid fluid when in the vapor state at a predetermined operatingtemperature, said gas also having a boiling point below that of saidfluid;

a chamber annularly disposed around the longitudinal axis of saidhousing and extending both radially outwardly of and longitudinallybeyond said housing;

wall means spaced from the outer surface of said housing for forming inconjunction therewith a cooling channel for allowing the removal of heatfrom said housing;

a plurality of throats extending into said channel for providingpassageways for the flow of inert gas and working fluid between saidhousingand said chamber;

third capillary wick means disposed within said chamber and saidthroats, substantially along a surface of said chamber and of saidthroats, said third capillary wick means being connected to said secondcapillary wick means; and

second electrically insulating wick means connecting said first and saidthird capillary wick means.

8. A heat pipe comprising:

a hermetically sealed housing of substantially tubular shape having aheat input portion and a heat output portion and an electricallyinsulating portion disposed between said input and said output portions;

first capillary wick means disposed within said housing substantiallyalong a surface of said heat input portion, second capillary wick meansdisposed within said housing substantially along a surface of said heatoutput portion, first electrically insulating wick means connecting saidfirst and second wick means;

a volatile working fluid contained within said housing and within atleast portions of said wick means;

a substantially chemically inert gas contained with said housing andhaving a dielectric strength greater than the dielectric strength ofsaid fluid when in the vapor state at a predetermined operatingtemperature, said gas also having a boiling point below that of saidfluid;

a chamber annularly disposed around and substantially longitudinallycoextensive with said housing, said chamber and said housing forming acooling channel for allowing the removal of heat from said housing;

a plurality of throats extending radially outwardly from said housingand into said channel for providing a passageway for the flow of inertgas and working fluid between said housing and said chamber;

third capillary wick means disposed within said chamber and said throatssubstantially along a surface of said chamber and of said throats, saidthird capillary wick means being connected to said second capillary wickmeans; and

second electrically insulating wick means connecting said first and saidthird capillary wick means.

PatmH1No. 3,563,309 Dated February 16, 1971 lnvmnmr(s) Algerd BasiulisIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

F551. 1, line 17, "gray" should be gravity-.

line 37, after "arrangements" insert are. Col. 2, line 16, after "he"insert in-. Col. 3, line 50, after "fluids" insert are:.

line 58, after "temperature" (first occurrence) insert range-. Col. 4,line 14, "hat" should be heat.

line 68, delete "Since the heat pipe" (first occurrence).

Col. 5, line 75, 241" should be 248". Col. 7, line 36, after "C F delete8".

line 37, "c F o" shguld be -C F line 42, afer "heat" insert -i%8ut andsald heat.

Signed and sealed this 26th day of October 1971.

EAL) test:

VARD M.FLETQHER,JR. ROBERT GOTTSCHALK- oestlng Offleer ActingCommissioner of Patents

1. A heat pipe comprising: a hermetically sealed housing having a heatinput portion and a heat output portion and an electrically insulatingportion disposed between said input and said output portions; firstcapillary wick means disposed within said housing substantially along asurface of said heat input portion, second capillary wick means disposedwithin said housing substantially along a surface of said heat outputportion, electrically insulating wick means connecting said first andsecond wick means; a volatile working fluid contained within saidhousing and within at least portions of said wick means; a substantiallychemically inert gas contained with said housing and having a dielectricstrength greater than the dielectric strength of said Fluid when in thevapor state at a predetermined operating temperature, said gas alsohaving a boiling point below that of said fluid; and means for enhancingseparation of said fluid in the vapor state and said gas when heat isbeing transferred from said heat input portion to said heat outputportion by means of said fluid.
 2. A heat pipe according to claim 1wherein said fluid is selected from the group consisting of Dowtherm A,FC43, Dowcorning 200, Freon 13, and Freon 12; and said inert gas isselected from the group consisting of N2, SF6, C3F8, C4F8, 8, C4F10 andC2F6.
 3. A heat pipe according to claim 1 wherein the volatile workingfluid contained within said housing is sufficient to substantiallysaturate each said wick means, and the quantity of said inert gasdisposed within said housing is sufficient to maintain electricalinsulation between said heat output portions at said operatingtemperature.
 4. A heat pipe according to claim 1 wherein the last namedmeans is an interface shield disposed within said output portion of saidhousing.
 5. A heat pipe according to claim 1 wherein the last namedmeans includes a chamber spaced from but operatively coupled to saidheat output portion such that said gas may pass from said housing intosaid chamber, whereby during the operation of said heat pipe said inertgas substantially resides in said chamber and said working fluidsubstantially resides in said housing.
 6. A heat pipe comprising: ahermetically sealed housing of substantially tubular shape having a heatinput portion and a heat output portion and an electrically insulatingportion disposed between said input and said output portions; firstcapillary wick means disposed within said housing substantially along asurface of said heat input portion, second capillary wick means disposedwithin said housing substantially along a surface of said heat outputportion, electrically insulating wick means connecting said first andsecond wick means; a volatile working fluid contained within saidhousing and within at least portions of said wick means; a substantiallychemically inert gas contained with said housing and having a dielectricstrength greater than the dielectric strength of said fluid when in thevapor state at a predetermined operating temperature, said gas alsohaving a boiling point below that of said fluid; a chamber annularlydisposed around the longitudinal axis of said housing and extending bothradially outwardly of and longitudinally beyond said housing; wall meansspaced from the outer surface of said housing for forming in conjunctiontherewith a cooling channel for allowing the removal of heat from saidhousing; and throat means extending into said channel for providing apassageway for the flow of inert gas and working fluid between saidhousing and said chamber.
 7. A heat pipe comprising: a hermeticallysealed housing of a substantially tubular shape having a heat inputportion and a heat output portion and an electrically insulating portiondisposed between said input and said output portions; first capillarywick means disposed within said housing substantially along a surface ofsaid heat input portion, second capillary wick means disposed withinsaid housing substantially along a surface of said heat output portion,first electrically insulating wick means connecting said first andsecond wick means; a volatile working fluid contained within saidhousing and within at least portions of said wick means; a substantiallychemically inert gas contained with said housing and having a dielectricstrength greater than the dielectric strength of said fluid when in thevapor state at a predetermined operating temperature, said gas alsohaving a boiling point below that of said fluid; a chamber annularlydisposed around the longitudinal axis of said housing and extending bothradially outwardly of and longitudinally beyond Said housing; wall meansspaced from the outer surface of said housing for forming in conjunctiontherewith a cooling channel for allowing the removal of heat from saidhousing; a plurality of throats extending into said channel forproviding passageways for the flow of inert gas and working fluidbetween said housing and said chamber; third capillary wick meansdisposed within said chamber and said throats, substantially along asurface of said chamber and of said throats, said third capillary wickmeans being connected to said second capillary wick means; and secondelectrically insulating wick means connecting said first and said thirdcapillary wick means.
 8. A heat pipe comprising: a hermetically sealedhousing of substantially tubular shape having a heat input portion and aheat output portion and an electrically insulating portion disposedbetween said input and said output portions; first capillary wick meansdisposed within said housing substantially along a surface of said heatinput portion, second capillary wick means disposed within said housingsubstantially along a surface of said heat output portion, firstelectrically insulating wick means connecting said first and second wickmeans; a volatile working fluid contained within said housing and withinat least portions of said wick means; a substantially chemically inertgas contained with said housing and having a dielectric strength greaterthan the dielectric strength of said fluid when in the vapor state at apredetermined operating temperature, said gas also having a boilingpoint below that of said fluid; a chamber annularly disposed around andsubstantially longitudinally coextensive with said housing, said chamberand said housing forming a cooling channel for allowing the removal ofheat from said housing; a plurality of throats extending radiallyoutwardly from said housing and into said channel for providing apassageway for the flow of inert gas and working fluid between saidhousing and said chamber; third capillary wick means disposed withinsaid chamber and said throats substantially along a surface of saidchamber and of said throats, said third capillary wick means beingconnected to said second capillary wick means; and second electricallyinsulating wick means connecting said first and said third capillarywick means.